The elimination of most anticholinesterases depends on the kidney, even if the main organ for their metabolism is the liver. Renal excretion of pyridostigmine, edrophonium and neostigmine accounts for 15%, 70% and 50%, respectively. In the absence of renal function, the serum half-life of neostigmine is prolonged, its plasma clearance is decreased However, the pharmacodynamics of neostigmine have not been determined in renal failure. This study was designed to compare the neostigmine dynamics in 18 patients with normal renal function to that in 18 patients with renal failure(Group I & II, respectively). Using the flexor carpi ulnaris EMG via ulnar nerve stimulation with Train-Of-Four(TOF) under the constant infusion of vecuronium to produce about 85%-twitch depression, the responses of neostigmine with three different doses were obtained. The results are follows; 1) The constant infusion rates of vecuronium to maintain sbout 15